Coal gasification is a process of converting coal to a synthetic gas by heating it alongside oxygen. This process avoids burning coal altogether, by forcing carbon molecules apart to create carbon monoxide and hydrogen gas. The Lurgi-Ruhrgas process is a well accepted process employed in electric power generation plants to convert coal to gas and utilize that gas to power machinery that generates electricity. Underground coal gasification is another process that converts coal that is still in the un-mined coal seam to gas. Injection wells are utilized to supply oxidants to the coal seams in order to facilitate the oxidation process and produce the gas. This process allows access to coal resources that are too deep, low grade or too thin to be recovered by other methods.
Coal gasification is a “clean technology” which essentially eliminates environmental air pollution. However, the remaining fly ash continues to be an environmental concern due to the concentrations of heavy metals and volatile organic compounds present in the ash. Heavy metals in fly ash, include arsenic, beryllium, cadmium, chromium, copper, lead, mercury, molybdenum, nickel, radium, selenium and vanadium, which in sufficient quantities are associated with cancer and other conditions detrimental to good health. Without proper protections, the contaminants can leach into ground water, which negatively impacts ecological systems and poisons drinking water.
In many such instances the treatment of such fluids can be extremely expensive. For example, in 2008 the Tennessee Valley Authority's Kingston Fossil Plant in Roane County, Tenn. spilled more than 1.1 billion gallons of coal fly ash slurry from a settling pond. The ultimate cost of the cleanup may be well over one billion dollars. Worldwide, the majority of fly ash produced from coal fueled power plants is disposed of in landfills and ash ponds.
The U.S. Environmental Protection Agency (EPA) estimates that approximately 100 million tons of fly ash is produced annually in the United States by over 500 power plants. As the demand for energy increases, so will the amount of fly ash produced. The discharge of fly ash as a solid or diluted in water is unacceptable unless treated. Currently, most fly ash is disposed of in landfills and holding ponds where they remain untreated.
Water is an important natural resource that needs to be conserved and preserved wherever possible. One way to accomplish that goal is to clean and recycle the by-products of coal based fuel processes. On site processing equipment, at the site, is the most cost effective and environmentally friendly way of recycling this natural resource.
Thus, what is needed is a process and apparatus suited for conditioning water contaminated with heavy metals and organic compounds such as fly ash.